A number of contemporary communications systems—for example, differentially encoded QPSK, 16 QAM, 64 QAM—employ differential encoding to achieve a robustness with respect to phase noise and channel impairments. As is known, such systems require a differential decoding operation at a receiver to recover transmitted information. Oftentimes, to achieve superior performance, a soft decision encoding/decoding (SDFEC) is also employed. A SDFEC decoder requires soft bit metric information for the bits at the differential decoder.
Accordingly, methods and apparatus that provide for the efficient generation of soft bit metric information from DE-QPSK symbols would represent a welcome addition to the art.